Nuclear fuel assemblies require particular procedures for their use, transport and even for disposal as waste. Thus, irradiated nuclear fuel assemblies from nuclear power stations have to be stored after use. Nuclear power plants are provided with a pool in which these assemblies are stored, but this storage is temporary and the nuclear fuel assemblies then have to be evacuated to safe so-called “final” or “interim” storage sites, and in particular including leak tight metallic confinements protected by concrete storage modules.
To transport them to their destination, leak tight confinements containing nuclear fuel assemblies need to be put into place in “temporary” radiation shielding receptacles. Therefore safety rules that impose confinement of nuclear fuel assemblies in a leak tight metallic receptacle are respected, the receptacle itself being placed in a package called the transfer package with radiation shielding walls. The metallic receptacle comprises essentially a hollow tubular body with a generally cylindrical shape with a circular cross section, equipped with a closed lower end and a completely open upper end. Document FR 2 805 655 describes an example of this technique.
One conventional possibility for positioning nuclear fuel assemblies in the metallic receptacle and in the transfer package is to use a “dry” or “hot” radiation shielding containment with remote manipulations of the different elements using manipulation arms: it is obvious that working people cannot be close to elements without any radiation shielding. The disadvantage of this method is its complexity, and consequently the time and cost, of the containment and also the tools and manipulation arms.
Since water is good radiation shielding and all power plants have a pool, it has been proposed to package the radiation material directly in pools. In this context, the metallic confinement receptacle is placed in the transfer package, the assembly is immersed in the pool and fuel is loaded into it. The loading opening is then closed off by a radiation shielding closing device that provides protection during the following steps consisting of closure, confinement and transport that take place dry: for example see FR 2 805 655. However, this technique is more restrictive because part of it has to be done while totally immersed in more than ten meters of water. Furthermore, to achieve maximum safety, it is essential to eliminate all residual water in receptacles before closing them, both in the metallic confinement receptacle and in the transfer package.
However it is possible that an additional confinement, subsequently called the “second confinement” is necessary in addition to the confinement provided by the leak tight metallic receptacle: a second additional containment needs to be put into place. Some legislation imposes this second double containment. In this case, conditioning under water has not been possible up to now, particularly due to problems with drainage of the second confinement containment.